Make-Up Air System vs. Recirculation Open Flame Heat
Problem: It has been stated that recirculation heaters save fuel cost vs. mechanical make-up air systems.
And, with built-in thermostats, recirculation heaters properly control the building conditions.
Outline of Project:
- Midwest hospital project. Heated through the winter of 2012 – 2013
- 7-story addition, plus basement with 20,000 sq ft each floor, for a total of 160,000 sq ft
- Fuel source is natural gas and 5-lbs pressure
- Building was split between east and west wings
- Construction heating located as follows:
- 70,000 sq ft (Floors 1 – 7)
- 40,000 sq ft (Floors 1 – 4)
- 20,000 sq ft
- Total building area to be heated is 130,000 sq ft.
- West side general schedule: Outer skin mid-December with permanent window January.
- East side general schedule: Outer skin end of December with permanent windows end of January
- Temporary windows installed into all openings as of November, 2012
Recirculation Heater - Contractor Promise:
- 9 recirculation heaters to complete construction heat requirements: $ 9,000.00
- Estimated fuel cost for using recirculating heaters: $ 30,000.00
Final Outcome - Using Recirculating Heaters:
- 14 recirculation construction heaters required to heat the building throughout the winter season
- Estimated end fuel cost, December thru mid-April ... $ 81,296.00 (meter start # 0000 / meter ending # 86,351)
(Difference paid by customer of $ 51,296 .00 in extra fuel vs. quoted budget at start of project)
- Temperature and humidity readings taken inside the project in March as example
- Outdoor readings 28.0°F, 46.0 % RH
- East wing readings (average) 50.0°F, 37.0 % RH * High RH area reading of 45 % RH
- West wing readings (average) 32.0°F, 53.5 % RH * High RH area reading of 59 % RH
- Central readings (average) 57.0°F, 35.0 % RH * High RH area reading of 56 % RH
What Could Have Been a Different Experience by Investing in Mechanical Make-Up Air Design ?
- 3 Mechanical make-up air construction heaters could have provided heat for the entire project
- Mechanical make-up air heaters would have been located outside building vs. Fourteen (14) open flame,
recirculation style heaters and associated temporary fuel hoses laying throughout the work space.
- Customer could have been provided with an up-front, realistic value of $ 80,000 - $90,000 for fuel costs
- Superior control over building temperature and humidity vs. recirculation heaters. As recorded, 78% swings for
average temperature and 51% RH swings for humidity levels throughout the inside of the building.
Mechanical make-up air designs hold a more constant even interior temperature and RH humidity with recorded averages of 38% - 44%. (20% lower moisture average RH vs. recirculation)
- Building materials perform better and final finish schedules stay on target when more control is provided
by the use of a properly designed mechanical make-up air system vs. recirculation open flame heat